1. Field of the Invention
This invention relates to a method for adjusting image brightness at the time of reproducing an image read from photo film or an image photographed with a digital camera as a photographic print or the like and to a system for implementing the method.
2. Description of the Related Art
One conventional method for adjusting the brightness of an image photographed with a camera or the like is autoexposure (AE). In generally adopted AE, desirable mean picture brightness is assumed to be equivalent to 18% reflectance and the diaphragm aperture and shutter speed of the camera are controlled to make the mean picture brilliance value equivalent to 18% reflectance.
One technique used to improve the exposure accuracy is to divide the picture into multiple regions and determine the final mean brilliance taking the mean values of the individual regions or differences between regions into account (as in center-selective light measurement, valuative light measurement and the like). Some cameras, particularly sophisticated single-lens reflex cameras, enhance exposure accuracy by additionally utilizing an autofocus function to detect the main subject.
The application of such techniques is not limited to the camera side. On the lab printer side, too, it is a common practice to adjust brightness by controlling the number of seconds of exposure when exposing the print paper so as to give the large area transmittance density (LATD) of the negative a print density corresponding to 18% reflectance (i.e., a print density of 0.75).
Since these methods postulate the mean image brightness to be 18% reflectance, however, they encounter problems when, for example, the pictures includes an object of very high or low brightness. Specifically, such objects markedly affect the mean value of the brightness and, as such, cause the image obtained to be excessively light or dark.